If the auto ac compressor clutch is not engaged, the fuse may be blown, the wire of the clutch coil is disconnected, the clutch coil is bad, the grounding is bad, or the low voltage lock. The AC compressor clutch obtains power in many ways. They can be activated by relays powered directly by the appropriate state of the low and high voltage switches. Alternatively, the relay can be operated by a PCM that explains the status of the low and high pressure sensors. In that case, the PCM will see that the refrigerant pressure is within limits, and the PCM will provide a ground connection to the control coil side of the AC compressor clutch relay. In both cases, you can start the diagnosis by checking the compressor clutch fuse.
In some vehicles, the compressor magnetic clutch relay is turned on and off by the low pressure switch and the evaporator temperature sensor.
In a computer-controlled system, the compressor clutch relay is grounded through the computer.
If the fuse is good, disconnect the electrical connector from the compressor clutch coil. Remove it from the moving parts so that the power supply and grounding can be checked safely. With the engine running and AC set to MAX, use a digital voltmeter to check the battery voltage and the grounding on the connector.
If there is no battery voltage, please pull the auto compressor clutch and check the power and ground on the relay control coil terminal in the socket.
Wiring varies by brand, model and year. Some car manufacturers use PCM or ECM to trigger the relay to control the coil to ground. In order to ground the computer, it is necessary to receive good signals from the low-voltage switch, the high-voltage switch and the evaporator temperature sensor.
In other vehicles, power flows through the air conditioner switch to the fuse, and from the fuse through the low voltage and evaporator temperature sensor to the clutch coil.
Post time: Nov-05-2020